This invention relates to superconductors and methods of manufacture thereof. It has particular reference to the insulation of superconductive wire. The standard method of manufacturing multi-filamentary intermetallic superconducting wires now comprises the steps of producing a precursor wire comprising filaments of one of the elements of the intermetallic compound embedded in a matrix of a carrier metal, usually copper, and the remaining components of the intermetallic compound. As intermetallic compounds are extremely brittle it is necessary to fabricate the precursor wire to its final diameter before heating the precursor wire to react the components of the intermetallic compound to form the superconducting filaments.
There are two main ways of producing wires from superconducting wire having intermetallic filaments therein. The first method is to react the wire first and then to wind the magnet from the reacted wire. Such a method is known as a react and wind (RAW) method.
The second method of manufacturing magnets is to wind the magnets with green or unreacted wire and to react the wire subsequent to the winding operation. Such a method is known as wind and react or WAR.
In British Pat. No. 1,413,795 there is described and claimed a method of insulating intermetallic superconductive wire which is particularly applicable to the RAW route. The method therein described basically entails the use of a stop weld to prevent the adjacent turns of a spool of wire from becoming welded together during the reaction stage. Because of the great lengths of wire which are reacted at any one time it is necessary to wind the wire onto a spool for insertion into a suitable furnace during the reaction. Thus, in the aforementioned British Pat. No. 1,413,795 there is described the use of a stop weld which comprises either carbon or magnesium oxide which can be brushed off of the wire after the reaction stage.
There is also proposed the production of an electromagnetic coil in a single operation by winding the coated precursor into a coil and reacting it with the insulant staying in position to prevent welding between the turns and also to act as an electrical insulant. It is stated that such a method is only usable where the stop weld is also an electrical insulant. The specification then goes on to state that the coil is then impregnated to hold the turns in position.
Although the methods described and claimed in British Pat. No. 1,413,795 are eminently suitable for the RAW route, it has so far not been possible to produce superconductor coils by the WAR route using the methods described in the aforementioned British patent specification. The reason for this is that there has to date been no known coating which is both flexible after coating and drying and yet insulating in the heat treated state.
The present invention provides in one embodiment thereof an insulant for superconducting wires which is flexible in the coated and dried state but which is insulating in the reacted or heat treated state.